(1) Field of the Invention
The present invention relates to a playback apparatus for playing a plurality of related contents, and in particular, relates to a technique for protecting copyright of the content.
(2) Description of the Related Art
Digital contents have begun to be distributed in increasingly diverse forms in recent years, one of which is distribution using virtual packages.
A virtual package consists of a plurality of media on which mutually related digital contents are respectively recorded. The digital contents recorded on the plurality of media are treated by a playback apparatus as being recorded in one package.
As one example, a content creator pre-distributes large-capacity content (main content) that is a movie whose script is in English to the owner of a content playback apparatus, using a BD-ROM. After the English script has been translated into Japanese, the content creator distributes small-capacity content (sub-content) that is Japanese subtitles of the movie, using an SD card. When the sub-content has been distributed, the owner of the playback apparatus is able to watch the movie containing the main content and the Japanese subtitles that are the sub-content as if they were one content recorded in one package.
Since digital content is easily copied without deterioration of the information, protection of copyrights of digital content is crucial, regardless of whether or not it is distributed as a virtual package. For this reason, in addition to recording digital content in an encrypted state on a recording medium, information that prevents the content from being decrypted with a playback apparatus key that has been exposed is written to the recording medium. This technique, which is disclosed in JP 2002-281013A, improves copyright protection by preventing the content from being decrypted with the exposed key from recording media distributed after the key has been exposed.
However, this copyright protection is structured such that decryption of encrypted content can be complete only in information in a package in which digital content is recorded. Consequently, such copyright protection is problematic in that part of the content of a virtual package can be played without having all the elements that make up the virtual package.
For example, sub-content on an SD card can be played with only the SD card, in other words, without the BD-ROM that is also an element of the virtual package. This contravenes the intention of the copyright owner who created the package.
In view of the stated problem, the object of the present invention is to provide a content playback apparatus that plays content recorded in a virtual package in a manner that assembles the components of the virtual package as intended by the creator, and protects the copyright thereof.